Prostate cancer has become the most commonly diagnosed form of cancer, and is the second leading cause of cancer death among males in the United States. There are about 125,000 new cases of prostate cancer reported each year and about 30,000 deaths from this disease. Boosting the efficacy of radiation therapy with hyperthermia (which is heating to above 43 deg.C) may improve the prognosis of prostate cancer patients, since there is a positive correlation between local control and disease-specific survival. Innovative microwave hyperthermia applicators for insertion into the urethra and rectum would be characterized by their three- dimensional pattern of power deposition for typical separations and angles encountered in the clinic. The ability of the applicators to focus energy deposition through use of driving-phase differences would be evaluated. The applicators would be used to heat perfused canine prostates, and the three-dimensional temperature pattern in this site would be quantified. The ability of the applicators' surface-cooling systems to protect the urethra and rectal mucosa would be evaluated. The histopathology of prostatic and periprostatic tissue would be correlated with local temperature. Disposable versions of the applicators suitable for commercial production would be developed.